Despite its rich biodiversity, Kielder Forest didn't exist a century ago. It was created to help provide the country with timber and has evolved to become a wildlife refuge.

It's winter in Kielder Forest and while some wildlife battles to survive, others sleep.

It's summer in Yorkshire and inside the county's largest forests, Dalby and Cropton, the lengthening days bring a surge of life. We meet the beaver family who were established in Cropton in 2019 as part of a scientific trial to see how they would change the landscape. They have since got to work building dams and creating the perfect watery environment for these amazing architects of the natural world to live in. We follow these incredible creatures as they progress over the summer. Elsewhere in the forest, the signs of the new season are all around. As the temperatures rise, there is a chance to be reacquainted with those animals absent from the forest over the winter. Some creatures have been asleep through the colder months, like Britain's only venomous snake, the adder, now out soaking up the heat of the sun. Birds return to Dalby after spending winter in Africa. There is an array of new life in the forest. A team of bird conservationists are on the lookout for nightjars: a bird that has made a perilous journey of thousands of kilometres to spend the summer in Yorkshire. They try to catch one in specially designed nets so they can ring it and collect data, but it is not such an easy task. Meanwhile, in a different part of the forest, the world's largest dry stone wall maze is being built. It's an epic project needing 5,000 tonnes of stone and years of careful building using this ancient precision craft. It's one man-made wonder amid this landscape of natural beauty.